The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In the field of an automatic transmission, more multiplicity of shift-stages is used to enhance fuel efficiency and drivability of a vehicle. The increase of oil price is triggering a hard competition in enhancing fuel efficiency of a vehicle.
The engine downsizing has been attempted for the purpose of weight reduction and fuel efficiency. Simultaneously, the development of more shift stages of an automatic transmission has been conducted to provide better drivability and fuel efficiency.
In order to achieve more shift-stages of an automatic transmission, the number of parts is typically increased, which may affect installability, production cost, weight and/or power flow efficiency.
An automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to seven control elements (frictional elements), and this causes a lengthy transmission, thereby deteriorating installability.
In this regard, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements has been considered. However, such an arrangement may not be widely applicable, and using dog clutches may easily undermine shift-feel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.